Process and device for producing turned parts from rods or bars

ABSTRACT

In order to fabricate turned parts (18) out of a steel rod or bar (13) solely by grinding, the latter is chucked in oppositely disposed collets (14, 16) and is ground by two profiled grinding discs (20, 20&#39;) which act on it either sequentially or simultaneously. The two profiled grinding discs are advanced to (and plunged into) the rod or bar (13) (for plunge-cut grinding) at an acute angle of attitude thereto, and said discs rotate on respective axes (D, D&#39;) which are inclined with respect to the axis (B) passing through the collects. In this way, surfaces (1&#39;, 5, 6, 8, 10) which are perpendicular to the longitudinal axis (A) of the rod or bar and which may even face in opposite directions can be produced without having to rechuck the turned part (18). The usual types of profiled turned part segments (1, 2, 3, 4, 7, 9) may also be produced at the same time.

The invention relates to a method of manufacturing profiled turned partswhich are symmetric with respect to their longitudinal axis, wherebyprofiled turned parts which may include right- and left-facing normalfaces can be produced from rods directly by grinding, without anecessity for a separate cutting-machining operation.

The invention also relates to a device for carrying out the above methodof manufacturing profiled turned parts.

It is known to produce profiled turned parts which are axially symmetricwith respect to their longitudinal axis by the method of machining rods(or bars) with a cutting tool. These rods are namely unhardened steelrods of round cross section. Turned parts produced in this manner, ifthey are to meet stringent requirements as to dimensional accuracy andaxial symmetry, they must undergo hardening followed by grinding todimensions.

This traditional technique, widely employed, e.g., in the clock industryand the fine machinery industry, has among its disadvantages the factthat relatively high rate of tool wear leads to a series of relativelylarge measurement deviations in the cut or lathed part, which deviationsneed to be corrected in the subsequent grinding operations. It has beensought to alleviate this known disadvantage by employing hard metaltools. However, there is another disadvantage which survives: In orderto sharpen (regrind) the cutting tools, they must be removed from thecutting machine, re-mounted, and readjusted, which is time-consuming andadds to the cost of precision parts (which are already costly tomanufacture). The dimensional differences in turned parts in a singleproduction run may be so great that it will be difficult to grind thehardened or unhardened parts to proper dimensions, and the grindingwheel must be applied very slowly to the parts, particularly in the caseof fine turned parts. This is because the rough dimensions differ sogreatly from piece to piece. A consequence of this is that there may besubstantial piece-to-piece differences in the time of the grindingoperation (from beginning of grinding to sparking out, which latter isthe point at which sparks cease); or there may be substantialdifferences in grinding depth from piece to piece, which can also beundesirable.

Accordingly, the underlying problem of the present invention is todevise a method and device which eliminate the disadvantages of thecustomary methods and devices for manufacturing turned parts, andproduce economical, precision, axially symmetric profiled turned parts.

This problem is solved according to the invention by a method and by adevice as set forth in the appended claims.

The invention enables high precision axially symmetric turned parts tobe produced from rods or bars, solely by grinding. This has not beenpossible heretofore. Often, the invention will enable grinding totolerance without any subsequent grinding step. Moreover, workpiecesused may be of already hardened steel, thereby avoiding a subsequenthardening and regrinding to tolerance.

Additional advantages and details of the invention will be apparent fromthe following description and the associated drawings, in which themanufacture of a particularly difficult to produce precision part isdescribed, which part has transverse shoulders, grooves, end faces, andthe like.

FIG. 1 is a side view of the turned part, enlarged;

FIG. 2 is a schematic top view of the arrangement of a first part of theinventive device, wherewith a first operation in the inventive method ofmanufacture the turned part is being carried out;

FIG. 3 is a schematic top view of the arrangement of a second part ofthe inventive device, wherewith a second operation in the inventivemethod of manufacturing the turned part is being carried out; and

FIG. 4 is a schematic top view of an arrangement of the inventive devicewherein the two parts of the device are combined, and the turned part issimultaneously ground by two profiled grinding discs.

FIG. 1 is an enlarged view of a turned part of a type which can bemanufactured by the inventive method, using the inventive device, solelyby grinding a round rod or bar of steel. The turned part is assumed tohave a length of c. 50 mm and a mean diameter of c. 4.8 mm, which mustbe ground to a tolerance of 0.005 mm and the ends of which can have amaximum out-of-round of 0.001 mm. Further, the two ends 1' and 10, aswell as the shoulder 5, the release transition 6, and the sides 8 of thegroove 7, are to be absolutely perpendicular to the longitudinal axis Aof the turned part.

It is not possible to manufacture such a turned part in a singleoperation by known techniques, particularly if the surfaces of theturned part must be finely ground. With the use of the invention,however, such a turned part can be manufactured from rod stock fullyautomatically. It is quite apparent what a substantial improvement theinvention affords in serial production of difficult to produce highprecision turned parts, in comparison to known manufacturing methods.The turned part illustrated has cylindrical regions, in particular anend pin 1, a release region 2, a large diameter region 3, and a smallerdiameter region 4. The surfaces which are to be ground preciselyperpendicular to the longitudinal axis A are an end 1', a shoulder 5, arelease transition 6, a groove side 8, and a second end 10. A groove 7separates the smaller diameter region 4 from the large diameter region3. One of the sides of groove 7 is inclined (9), and the other isperpendicular (8).

One skilled in the art appreciates that the illustrated part chosen as arepresentative workpiece for illustrating the invention is a verydifficult part to produce by ordinary methods and with ordinary devices;that it would be very costly to produce such turned parts in serialproduction by means of the customary method of cutting (lathing) andstepwise grinding of the various diameters, shoulders, ends, and angles;and that multiple chucking and handling of each turned part would berequired. Accordingly, the turned part illustrated is well suited todemonstrating the advantages and potential of the present invention incomparison to the manufacturing means ordinarily employed for suchturned parts.

In evaluating the advantages afforded by the invention over the state ofthe art, one must start with the fact that in any manufacturing methodaccording to the state of the art a rough-cut workpiece will be firstturned in a cutting (lathe) operation, from an unhardened steel rod orbar. The workpiece will then be hardened, and will be ground in a seriesof grinding operations. The first time the rough-cut workpiece ischucked the end pin 1, release region 2, large diameter region 3, end1', shoulder 5, and release transition 6 are ground; then in a secondchucking the small diameter region 4, groove side 8, and end 10 areground. With this procedure it is nearly impossible to ensure the axialprallellness required, and to ensure that the tolerance specified forout-of-round will be met, because when the release region 2 and shoulder3 are ground the workpiece is in a different chucking than when thesmall diameter region 4 is ground.

FIG. 2 shows a round rod 13 which may be comprised of unhardened orhardened steel, which rod 13 is extended through a first collet 14 ofthe tool headstock 15. The turned parts are to be fabricated from thissingle rod, in sequence. A second collet 16 is disposed opposite collet14 on the same axis B, in a synchronous tailstock 17. The rod 13 (or aturned part 18 still connected to the rod 13) is inserted in collet 16up to a detent 19 which can be adjustably fixed in place.Advantageously, the headstock 15 and the synchronous tailstock 17 arecomponents of a numerically controlled grinding machine, so that alloperations and movements can be controlled automatically.

Also shown in FIG. 2 is a profiled grinding disc 20 and a steadyingpiece 21. The axis B between the collets, which axis coincides with thelongitudinal axis A of the turned part into which the rod 13 is beingground, is not perpendicular to the direction of advance (double arrowC) of the profiled grinding disc 20 but is at an oblique angle thereto.The rotational axis D of the disc 20 is correspondingly inclined withrespect to the longitudinal axis A of the turned part 18, i.e., 18', andthe axis B. An inclination of c. 10° has proven advantageous. Thisenables correspondingly inclined portions of the profiled grinding disc20 to be used to correctly grind surfaces on the turned part whichsurfaces are to be perpendicular to the longitudinal axis A, e.g. theend surface 1', the shoulder surface 5, and the release transitionsurface 6, whereby the ground surfaces are truly perpendicular to axis Aof the turned part.

Advantageously, the grinding disc 20 is configured such that it cangrind the following surfaces in a single working step (although possiblywith a plurality of passes): the end pin 1, the release region 2, thelarge diameter region 3, the normal surfaces to region 3 (here theshoulder 5 and the release transition 6)--of a first turned part 18';and the end face 1' of the turned part 18 which has been completedexcept for the end face 1' and has been advanced into the second collet16. The small diameter region 4 can also be pre-ground in this step.Additionally, the small diameter region 4 of a third turned part, namelyof a turned part still essentially disposed in the first collet 14, maybe pre-ground in this step. In order to prevent deflection of thecurrently being ground turned part 18 away from the axis B, which wouldlead to dimensional errors, the steadying piece 21 is suitably disposed.

A second working step can be carried out with the rod 13 still chuckedas before in collet 14 (and where again a plurality of passes maypossibly be employed). In this step (FIG. 3), the side 8 of the grooveand the end face 10 are ground by a second profiled grinding disc 20'.Final grinding of the small diameter region 4 may also be performed inthis step. The grinding disc 20' is inclined with respect to thelongitudinal axis A of the turned part 18, as was disc 20, however inthis instance the inclination of the rotational axis D' of disc 20' isthe mirror image of the axis D of disc 20, with respect to the normalplane to the axis B connecting the collets.

As soon as the workpiece 18' has been fully pre-ground and the end face1' of turned part 18 has been completely ground, advantageously thesecond collet 16, in the synchronous tailstock 17, is opened and isretracted such that turned part 18, which has been partially inserted incollet 16 and has now been separated from rod 13, can be ejected fromcollet 16 by the detent 19, after which the rod 13 is advanced until theturned part 18' (still connected to rod 13) has been moved into theformer position of turned part 18 in the second collet 16. Then theabove-described two-step grinding operation is carried out again,possibly after a preliminary retraction of the grinding discs 20 and20'. Thereby a third turned part is pre-ground and turned part 18' isfinal-ground.

It may be advisable to check a critical diameter of the turned partduring the grinding process, by means of a diameter-measuring head 22,with the measurement then being used to control the advance of theprofiled grinding disc.

The turned parts fabricated according to the described grindingoperation, if ground from hardened rods 13, are now finished products,and need no further treatment. Even if the turned parts 18 are groundfrom unhardened rods 13, their dimensions are more accurate and thesurfaces are finer than if they had been fabricated by a cutting (lathe)operation. Nonetheless, it may be necessary to further machine themafter hardening, in order to ensure the required precision. In such acase the turned parts 18 will be provided with slightly oversizeddimensions, and will be ground to size only in the final grinding.

It may be advantageous to combine the two working steps (which weredescribed in connection with FIGS. 2 and 3) into a single working step,such that the profiled grinding discs 20 and 20' are applied to the rod13 (or the turned parts 18' and 18) from mutually opposed positions.This variant of the invention is illustrated in FIG. 4.

One skilled in the art will appreciate that the inventive method anddevice enable a turned part to be produced with a single chucking (andtwo working steps) which would require two chuckings to produceaccording to customary methods. It is obvious that the inventive methodand device enable manufacture of other turned parts than the partdescribed here which is manufactured economically and with a singlechucking. To do so it is sufficient to adjust the profiled grindingdiscs 20 and 20', and if necessary the steadying piece 21, to the givenconditions. There is nothing novel or nonobvious in making suchadjustments.

If an automatic device for the feeding of rods in succession is used,the manufacture of turned parts according to the invention can be fullyautomated, without need for manual adjustments of the grinding tools,because the profiled grinding discs can be honed directly while on thenumerically controlled grinding machines, by means of diamond rollers,and can be automatically realigned, as is known in the art.

If coiled material is used instead of straight rod or bar as thestarting stock for the manufacture of turned parts, which is apossibility due to the much lower rpm which is required for a groundpiece in comparison to a cutting-machined piece, fully automaticmanufacturing of parts can be set up to continue autonomously for days,without human intervention. This is not an achievable option withcutting machine (lathe) operations, because such operations invariablyrequire a subsequent grinding stage to sharpen the cutting tool, whichgrinding is carried out outside the machine, followed by handreadjustment.

Individual steps of the inventive method, and components of theinventive device, may be modified as required by the characteristics ofthe parts being fabricated.

I claim:
 1. A method of manufacturing profiled turned parts which aresymmetric with respect to their longitudinal axis (A), with the startingstock being rods or bars, whereby a rod or bar (13) from which theturned parts (18) are to be fabricated is advanced on a collet axis (B)joining first and second collets, said advancing proceeds through saidfirst collet (14) in a headstock (15) of a grinding machine comprised ofat least the said headstock (15) and a synchronous tailstock (17), withsaid advancing continuing into said second collet (16) disposed in thesynchronous tailstock (17), and said rod or bar is then ground by aprofiled grinding disc (20) which can be advanced transversely withrespect to said rod or bar; characterized in that the profiled grindingdisc (20) is rotated around an axis (D) which is inclined with respectto the collet axis (B), and is advanced against the rod or bar (13) atan acute angle, such that faces (1', 5, 6) which are perpendicular tothe longitudinal axis (A) of the rod or bar can be produced by plungingthe said disc into the rod or bar (13) in a plunge-cut grindingoperation; and in that a second profiled grinding disc (20'), alsohaving a rotational axis (D') which is inclined with respect to thecollet axis (B), is advanced against the rod or bar at an acute anglewhereby it is possible to produce opposite transverse faces (8, 10) onthe rod or bar (13) which faces are perpendicular to the axis (A) of therod or bar.
 2. A method according to claim 1; characterized in thatprofiled grinding discs (20, 20') are used which can grind other profileregions into the rod or bar (13) in addition to the transverse faces(1', 5, 6, 8, 10).
 3. A method according to claim 1; characterized inthat the two profiled grinding discs (20, 20') grind the rod or bar (13)in respective successive working steps.
 4. A method according to claim1; characterized in that the two profiled grinding discs (20, 20') grindthe rod or bar (13) simultaneously, acting from opposite sides thereof.5. A method according to claim 1; characterized in that one or both ofthe profiled grinding discs (20, 20') simultaneously grind(s) two turnedparts (18, 18') which can be fabricated from the rod or bar (13).
 6. Amethod according to claim 3; characterized in that at least one part ofthe rod or bar (13) is supported by a steadying piece (21).
 7. A methodaccording to claim 1; characterized in that the part (18') of the rod orbar (13) which part is disposed in the second collet (16) is severedfrom the rod or bar by a profiled grinding disc (20).
 8. A device forcarrying out the method of claim 1 on a grinding machine, comprised ofat least one headstock (15) with a first collet (14), further comprisedof a synchronous tailstock (17) disposed opposite the headstock (15) onan axis (B), and a second collet (16); characterized in that the subjectdevice is further comprised of at least two profiled grinding discs (20,20') which are individually or jointly controllable and fixable,wherewith said discs are disposed such that their rotational axes (D,D') are inclined with respect to the longitudinal axis (A) of the turnedparts (18) which are being fabricated out of the rod or bar (13), andsaid discs can be advanced to and plunged into the rod or bar (13) forplunge-cut grinding while said discs are at an acute angle of attitude.9. A device according to claim 8; characterized in that a translatabledetent (19) for the rod or bar (13) is disposed in the synchronoustailstock (17).
 10. A device according to claim 8; characterized in thatthe two profiled grinding discs (20, 20') are oppositely disposed withrespect to the longitudinal axis (B) passing through the collets.